Pectinesterase in the treatment of fruit and vegetables

ABSTRACT

A method to prepare a food containing a gel of a low-methoxylated pectin of at least one fruit or vegetable is disclosed. The method comprises adding pectin esterase to the fruit or vegetable or to the pulp thereof in an amount effective to demethoxylate pectin, optionally adding calcium chloride, and maintaining the fruit or vegetable or pulp under conditions such that the pectin esterase converts high-methoxylated pectin of the fruit or vegetable or pulp to low-methoxylated pectin and the low-methoxylated pectin forms a gel. The fruit or vegetable or pulp is then formulated to obtain the desired food containing the gel. The method is used, for instance, to produce fruit and vegetable jams and jellies, compotes, sauces and soups.

TECHNICAL FIELD

The present invention relates to the use of pectinesterase (E. C.3.1.1.11) in the preparation of food containing fruits or vegetables.Specifically, the invention relates to the use of pectinesterase in thetreatment of fruit or vegetables that is in the demethoxylation ofpectin. The treated fruits or vegetables are then used in thepreparation of jams, jellies, compotes, sauces and soups. The presentinvention further discloses a modification to the standard US applesauce preparation process.

BACKGROUND OF THE INVENTION

Fruit and vegetable jams and jellies are normally prepared by cookingprotreated fruit and subsequent cooling. The pectin present in the fruitgelates, thereby giving the jam or jelly its rheologicalcharacteristics. The pectin is mainly responsible for this gel formationdue to its gelifying power. The gelifying potential of pectin isdependent on several conditions, mainly:

dry substance content or brix,

pH of the fruit or vegetable,

concentration of pectin normally present,

degree of methylation of the pectin.

Pectins are major constituents of the cell walls of edible parts offruits and vegetables. The middle lamella which are situated between thecell walls are mainly build up from protopectin which is the insolubleform of pectin. Pectins are considered as intercellular adhesives anddue to their colloid nature they also have an important function in thewaterregulation of plants. Waterbinding capacity is greatly increased bythe amount of hydrophylic hydroxyl and carboxyl groups. The amount ofpectin can be very high. For example, lemon peels are reported tocontain pectin upto 30% of their dry weight, orange peels contain from15-20% and apple peels about 10% (Norz, K., 1985. Zucker und SusswarenWirtschaft 38 5-6).

From a chemical point of view pectin consist of methoxylatedpolygalacturonic acid residues. Pectins are classified in differemtcategories based on the degree of esterification and the degree ofpolymerisation.

On the basis of the degree of esterification pectins are divided intotwo groups:

1) high-methoxylated pectins with a degree of esterification higher than50%, and

2) low-methoxylated pectins having a degree of esterification lower than50%.

Both of these groups are capable of forming gels, however these gelsdiffer in the mechanism by which they are formed. The high-methoxylatedpectins form gels based on dehydration and electrical neutralisation ofcolloidal pectin-agglomerates. Gelation is stimulated if the pH is about3 (dependent on the fruit or vegetable in question) and sugar, neededfor the dewatering, is present in more than 60% dry weight. Depending onthe fruit, in practice, this often means that both sugar andhigh-methoxylated pectin have to be added to obtain the classical highsugar content jams. Structure forming interactions in thehigh-methoxylated pectin containing gels is based on hydrogen bondformation.

The low-methoxylated pectins are capable of forming gels with calciumions or other divalent cations only. Gel formation with low-methoxylatedpectins is based on ionic interactions. Calcium ions are naturallypresent in for example apples. No sugars have to be added in order toobtain suitable gelling properties. The amount of sugar and the pH inthis case only influence the speed and temperature of gelifying.Low-methoxylated pectins are therefore perfectly suited for thepreparation of low sugar content jams and jellies.

In practice pectin from fruits and vegetables generally has a highdegree of methoxylation which necessitates the addition of large amountsof sugars to obtain suitable rheological characteristics. Furthermore,the degree of methoxylation varies with the time elapsed between theharvesting and the processing of the vegetables or fruit. This leads toa difference in the viscosity of the produced jams and jellies if theprocessing conditions are kept constant.

SUMMARY OF THE INVENTION

The present invention discloses the use of pectinesterase in thepreparation of food containing fruits or vegetables. Specifically, theinvention discloses the use of pectinesterase in the treatment of fruitor vegetables that is in the demethoxylation of pectin. The treatedfruits or vegetables are then used in the preparation of jams, jellies,compotes, sauces and soups.

The pectinesterase is used to demethoxylate the high-methoxylatedpectins to obtain low-methoxylated pectins. The pectins obtained in thismanner show calcium dependent gelation. This gel formation does notrequire the addition of sugars.

The present invention discloses jams and jellies obtained after the useof pectinesterase.

Furthermore, the present invention discloses a method for treating thecrude fruit products with pectinesterase.

The present invention also discloses a process for obtaining apple saucecomprising the use of pectinesterase. Furthermore, the present inventiondiscloses how the characteristics of the apple sauce are improved usingpectinesterase in the standard US apple sauce preparation process. Theinvention also discloses how this standard process can be improved by aslight alteration in the process i.e. the introduction of a holding tankat a certain process stage.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic presentation of the apple sauce preparationprocess as used in the USA. The holding tanks 1) and 2) are suggestedmodifications to the standard process.

DESCRIPTION OF THE INVENTION

The present invention discloses the use of pectinesterase in thepreparation of food containing fruit or vegetables. The presentinvention discloses a method for preparing food containing fruit orvegetables comprising the addition of pectinesterase to the fruit orvegetable or to the pulp thereof to demethoxylate the pectin, andoptionally, the addition of calciumchloride allowing the mixture to forma gel and further formulating the so-treated fruit or vegetable toobtain the desired food.

Preferably, the fruit or vegetable is selected from the group of fruitsor vegetables containing high-methoxylated pectins.

Specifically, the invention is used in the preparation of fruit andvegetable jams and jellies, compotes, sauces and soups.

The inventors demonstrate that it is possible to treat crude fruit orvegetable products with pectinesterase, that due to this treatment thedegree of methoxylation of the pectin is lowered and that the resultingpectin gelifies with the calcium that is present in the fruit orvegetable. If the gelling is not complete it is possible to add highmethoxylated pectin before enzyme addition or to add low-methoxylatedpectin.

This process works well with fruits or vegetables which containhigh-methoxylated pectins, such as apple, strawberry, blackcurrant,orange, peach, pear, apricots and raspberry.

In the present invention both-strawberries and apples were used. Thefirst since it is a popular jam species and the second for its highcontent of high-methoxylated pectins.

Pectinesterases suitable for performing this process can be obtainedfrom different sources. The pectinesterase of the present invention canbe any pectiaesterase from plants, bacteria or fungi, suitable for thedegradation of high-methoxylated pectin. Preferably, the pectinesteraseis from fungal origin. More preferably, the pectinesterase is obtainedfrom Aspergilli, especially preferred is the use of pectinesteraseobtained from Aspergillus niger.

In a most preferred embodiment purified pectinesterase is used. Thispurification can be performed in different ways.

The crude enzyme may be purified for example by liquid chromatography(ion exchange, gel filtration, affinity) (Ishii et el., 1980. DeutschesPatentamt Auslegeschrift 2843351) or by selective inhibition of thepectin depolymerases (pH shock, heat shock, chemical inhibitors,chemical or organic solvents extraction) (Smythe C. et el., 1952. U.S.Pat. No. 2,599,531) Another source for obtaining purified pectinesteraseas defined for the present application is pectinesterase obtained byrecombinant DNA technology. An example of the use of recombinant DNAtechnology is the expression cloning of the Aspergillus nigerpectinesterase. The cDNA sequence of this gene has been reported (Khanhet el. Nucl. Acids Res. 18 4262 (1990)). As expression host Aspergillusniger could be used. However, in view of the possible contamination ofthe pectinesterase with polygalacturonase, pectin lyase and other pectindepolymerases it may be preferable to use a heterologous host organismfor producing the pectinesterase.

Suitable host organisms include bacteria and fungi. Preferred speciesare Bacilli, Escherichia, Saccharomyces, Kluyveromyces and Aspergilli.

The pectinesterase treatment of the present invention can be performedon entire fruits or vegetables, it can also be performed on presliced orground fruits or vegetables. The pectinesterase treatment of fruit orvegetables is performed as follows;

pectinesterase is added to the crude or pretreated fruit or vegetable,the amount may vary as long a clear effect on the viscosity of the finalproduct is detectable. Effective amounts, as shown for example inExamples of the present invention range from about 30-500 PE units perkg. These values merely serve as indications. It is understood that theeffect of pectinesterase does not only depend on the amount of enzymeadded but also on the time the enzyme performs its activity.

also required for obtaining the desired gels is the addition of cations.In the present description this is illustrated by the use ofcalciumchloride. Again calcium ions are to added in effective amounts.In Example 1 this is 250 ppm in the form of calciumchloride.

the temperature of the reaction is not critical and may range from10°-70° C.

reaction time again is not critical. Under application conditions it isdesirable to keep reaction times low, for economical reasons. It isshown that a reaction time of about 10 minutes leads to a considerableimprovement in the quality of apple sauce.

finally the reaction is stopped by heat inactivation of the enzyme. Thisinactivation may coincide with the sterilisation of the product beforecanning or packaging.

The treatment leads to an increased firmness and viscosity of theproduct. After enzymatic treatment the fruits or vegetables can be addedto dairy, bakery or confectionary products such as yoghurts, ice creamsor desserts. The products can also be used as jams or jellies orfillings for chocolates, cakes or sweets. Another use is in the coatingof other food products. By treating entire fruits or vegetables prior tofreezing the firmness of the fruits or vegetables after defreezing isincreased. The pectinesterase treatment can also be used to improve thefirmness of the entire fruits or vegetables. Pectinesterase treatmentbefore blanching or cooking can be used to retard or prevent softeningof the fruit or vegetable.

Retarding vegetable softening by cold alkaline pectin deesterificationbefore cooking has been reported (van Buren and Pitifer. J.Food Sci. 571022-1023 (1992)) and it is to be expected that enzymaticdeesterification also retards the indicated softening.

Apart from the direct uses of the treated fruit or vegetables asmentioned above, the application of the low-methoxylated pectinsdiminishes or abolishes the required use of sugars or other gelifyingagents. After treatment of high-methoxylated pectin containing fruits orvegetables with pectinesterase the use of texturing agents such asexogenous pectin or of gelling or thickening agents obtainable fromhigher plants, seaweeds, animals or microorganisms (such as alginate orcarageenan) can be largely diminished.

A further advantage of the use of gels from low-methoxylated pectins isthat in comparison with high-methoxylated pectin gels the gels areirreversible. This means that heating and subsequent cooling does notdestroy the gel. This heating and cooling is responsible for thewell-known increase in fluidity of the jams upon storage. To the expertin is clear from the above that pectinesterase may be used in anyfoodstuff where low-methoxylated pectins normally are applied. Examplesof such foodstuffs are apart form the mentioned jams and jellies allkinds of fruit fillings, glazes and aspics. Instead of usinglow-methoxylated pectin as such the low-methoxylated pectin can beobtained by in situ formation from high-methoxylated pectins through theaction of pectinesterase. In principle the formation of the (partially)demethylated pectin can be performed during any phase of themanufacturing process.

The present invention is illustrated by treatment of apples andstrawberries with pectinesterase and it is shown that the viscosity isconsiderably increased after using the demethoxylating enzyme thiseffect is even more pronounced upon the addition of calciumchloride. Thegelfirmness, measuresed as grams of counterpressure using a StevensTexture Analyser, increases upon treatment with pectinesterase. Byadding calciumchloride the firmness can even be increased more.

In other examples it is shown that under normal processing conditionsthe viscosity of apple sauce is increased following treatment withpectinesterase.

Use of pectinesterase leads to a better consistency as measured by theflow ring method. Consistency is an important measure for the quality ofapple sauce. Other improvements related to the use of pectinesterase inapple sauce preparation process are, a better mouthfeel and the absenceof free run juice.

The results of the industrial trials indicate that pectinesterase can beused with its profitable effect without any alterations to the presentproduction process.

The incorporation of pectinesterase in the present US standard applesauce production process, without altering the process as such, leads toa very short reaction time for the pectinesterase (80-120 seconds). Evenwith this short reaction time pectinesterase gives clearly favorableeffects on the product quality. This prompted the inventors to study theeffect of a longer reaction time of the pectinesterase on the quality ofthe apple sauce. Bench-scale experiments indicated that increase of thereaction time to about 10 minutes increases the product quality evenmore.

Therefore, as another aspect the present invention discloses an alteredproduction process for the preparation of apple sauce. The alterationconsists of the introduction of a holding tank in the apple saucepreparation process in order to increase the effective reaction time ofpectinesterase. It is suggested to keep the holding tanks under nitrogenand ad room temperature if positioned at position 1) at position 2) thetemperature is preferably about 60° C. The prefered holding time isabout 10 minutes and the volume of the tank should be chosenaccordingly. The present invention therefore discloses a process forpreparing apple sauce whrein the following steps are performed;

1) washing of apples,

2) sorting to remove bad apples,

3) peeling and removal of the core,

4) sorting to remove bad apples,

5) crushing, chopping or slicing of the apples,

6) hopping of the apples to the cooker,

7) steam cooking of the apples,

8) finishing i.e. removing of stamens, peels, seed and other undesiredparticles,

9) addition of sugar,

10) canning,

characterized in that pectinesterase is added to the apples aftercrushing, chopping of slicing of the apples.

In an improved version of this process a holding tank is addded afterthe enzyme addition step and before the steam cooking step. The holdingtanks are preferably kept under nitrogen and the holding time, whichvaries with the temperature, the amount of enzyme added and the desiredapple sauce consistancy.

The use of pectinesterase in the apple sauce process allows for theproduct/on of top (constant) quality apple sauce during the wholeseason. As mentioned before the degree of methoxylating changes with thetime after harvesting. The quality of the apple sauce using a standardprocess thus depends on the freshness of the fruits used in the process.Enzymatic demethoxylation leads to a constant and reproducible degree ofmethoxylation and thus to a constant quality gel or apple sauce.

EXAMPLES Experimental

Assay of pectin esterase activity

One PE unit as used in the present specification is defined as theamount of enzyme which hydrolizes one microequivalent carboxymethyl inone minute under reaction conditions at 30° C. and pH=4.5. The substrateis Apple pectin Ruban Brun 0.5% with a methylation degree of over 70% inwater.

One PE Unit=0.98 PE International Unit. Experiments are performed withpectinesterase which is preferably free from pectin lyase andpolygalacturonase activities. Purification can be performed by standardmethods as mentioned in the description.

EXAMPLE 1

Pectinesterase treatment of fruit and influence on firmness

In the present experiments strawberries and apples were used.

Strawberries, without the green pans, were ground using a Waring blenderfor 30 seconds at low speed.

Apples; a blend of 33% Golden Delicious, 33% Red Delicious and 33%Granny Smith were first cut into small pieces, without the stem.Subsequently the apples were strained with the aid of a Roto shredderfixed on a Hobart mixer (model N-50G, speed 2). The mass was thengrinded, for 30 seconds (high speed), using a Waring blender (model32BLB0).

The fruit pulp (strawberries and apples were treated in the same manner)was devided into six portions of 300 grams and each portion was pouredinto an erlenmeyer flask.

Pectinesterase (240 PE units/g) was added to the pulp in two differentconcentrations. As can be seen in Table 1, flasks 1 and 2 were blanks.Flasks 3 and 4 contained 250 PE units/kg and flasks 5 and 6 contained500 PE units/kg.

The flasks were placed in a waterbath (50° C.) and stirred using amagnetic stirrer. After one hour, calciumchloride was added to flasks 2,4 and 6 and enzyme activity was stopped by placing all erlenmeyers in aboiling waterbath for 2.5 min.

Finally, the hot pulp was poured into plastic cups (300 ml) and left tostand for 24 hours at room temperature.

Firmness of the jellies was measured with the aid of a Stevens TextureAnalyser. Thereto a cylindrical plunger (TA4 1,5 inch) is brought intothe gel at a constant speed (0.5 mm/s). Firmness is defined as the forcerequired (in g) to penetrate the gel for a specified depth (5 mm).Duplicate measurements were performed. Results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Gelfirmness in grams counterpressure for penetration of 5 mm.                 Flask                Strawberry Apple                                         ______________________________________                                        1    Blank pulp          13         45                                        2    Blank pulp + 250 ppm CaCl.sub.2                                                                   13         45                                        3    Pulp + 250 PE u/kg  73         121                                       4    Pulp + 250 PE u/kg  56         250                                            + 250 ppm CaCl.sub.2                                                     5    Pulp + 500 PE u/kg  126        144                                       6    Pulp + 500 PE u/kg  117        249                                            + 250 ppm CaCl.sub.2                                                     ______________________________________                                    

The low firmness of flasks 1 and 2 indicates that gelification hasoccurred.

Flask 3 shows that gelification takes place in both apple andstrawberries after addition of pectinesterase. Higher PE concentrationslead to increased firmness (flask 5).

The influence of calcium on gelification clearly depends on the type offruit. The relatively low calcium concentration of apples, apparentlyinhibits a quick gelification of the high concentration of demethylatedpectin. Addition of calcium then increases the gel strength and the rateof gelification.

In strawberries the calcium concentration is relatively high, incombination with a low pectin concentration the addition of calciumresults in a non-optimal calcium pectin ratio. This leads to a lower gelstrength.

EXAMPLE 2

Influence of pectinesterase treatment on viscosity of apple sauce underlarge-scale processing conditions

In a typical large scale (3-5 tons) process the apples (Goldendelicious) are washed and ground. The temperature of this pulp isbrought to 90° C. by addition of fresh pulp to pulp kept at 94° C. in aratio of 1:9 (the so-called Hot-break process). The pulp is kept at 90°C. for 10 to 15 min before further processing.

Rapidase™ 9236 was added during the grinding at 150 g/ton and at 300g/ton. Viscosity was measured by taking samples at different times andcooling these samples to a standard temperature. Subsequently, thesesamples were applied on a plate having a fixed inclination and thedistance travelled by the front of the pulp was measured after 1 or 2minutes. The distance is a measure for the viscosity of the sample.

Results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Dose       150 g/ton        300 g/ton                                         Rapidase 9236                                                                 Temp. of   33° C.                                                                         21° C.                                                                              21° C.                                 measurement                                                                              distance (mm) measured after                                                  1 min.  1 min.   2 min.                                                                              1 min. 2 min.                               ______________________________________                                        Time of                                                                       measurement                                                                   after start                                                                   of PE addition                                                                 0         40      34       38    29     32                                   20         35      30       34    30     31                                   25         30      27       30    25     28                                   30         30      26       29    27     29                                   35         30      25       30    28     30                                   40         31      26       30    29     31                                   45         33      27       31    30     31                                   55         34      30       34    28     30                                   ______________________________________                                    

It can be calculated that the pulp was fully mixed with enzyme between25 and 40 minutes. After and before these times the pulp was increasingrespectively, decreasing in amount of pectinesterase.

It can be concluded that viscosity increases due to pectinesterasetreatment under processing conditions. With 300 g/ton the increase inviscosity was less then expected probably due to an overdosage ofpectinesterase with a concurrent lack of a sufficient amount of calcium.

EXAMPLE 3

Use of pectinesterase in an industrial process for production of applesauce

Enzyme preparation

In the present example pectinesterase from Aspergillus was used theenzyme had an activity of 260 PE units/g.

Viscosity measurement

Viscosity measurement was performed using the flow ring (via flow) asrecommended by the USDA (United Sates Department of Agriculture).

Free run juice measurement

Free run juice was estimated visually. Quantities are indicated asfollows:

+++a lot of free run juice

++medium amount of free run juice

+small amount of free run juice

-no free run juice

Mouthfeel test

The mouthfeel is graded by tasting. The following gradations are given:

poor taste

medium taste

good taste

very good taste

Description of the industrial apple sauce preparation process

Industrial apple sauce preparation is performed by the followingprocessing steps. The process described is the one normally used in theUSA. This process differs from the one used in Europe. The process isschematically presented in FIG. 1.

Description of the process for apple sauce preparation in the USA

The process for apple sauce preparation comprises the following steps:

1) washing of apples

2) 1st sorting to remove bad apples

3) peeling and removal of the core

4) 2nd sorting to remove bad apples

5) crushing )

chopping ) different types of crushers

slicing )

6) hopper conveyor--conveyor to cooker

7) steam cooker--pulp heating to 93°-94° C.

8) finisher--removing of stamens, peels, seed and other undesiredparticles

9) bulking tank for sugar addition

10) canning line

Experiments

Three trials were performed at industrial scale. Pectinesterase wasadded during transport of the sliced apples on the conveyor to thecooker. Effective reaction time for the pectinesterase was thereforevery short, 80-120 seconds. The temperature during the reaction on theconveyor was 60° C. As mentioned before the mixture was heated by mixingwith a mixture of 93°-94° C. in a ratio of 1:9.

I. Contact time enzyme (max): 80 seconds.

Medium quality of apples, chopper: coarse paticles.

Enzyme 1200 g/ton apples.

Temperature 60° C. at the place of addition.

    ______________________________________                                                  Average Free run                                                              consistancy                                                                           juice       Mouthfeel                                       ______________________________________                                        No enzyme   6.37      ++          ND                                          (before test)                                                                 With enzyme 6.01      +           ND                                          No enzyme   7.04      +++         ND                                          (end of trial)                                                                ______________________________________                                    

II. Contact time enzyme (max): 120 seconds.

Good quality of apples, chopper: small paticles.

Enzyme 1000 g/ton apples.

Temperature 60° C. at the place of addition.

    ______________________________________                                                  Average Free run                                                              consistancy                                                                           juice       Mouthfeel                                       ______________________________________                                        No enzyme   5.9       -           good                                        (before test)                                                                 With enzyme 5.4       -           very good                                   No enzyme   5.9       -           good                                        (end of trial)                                                                ______________________________________                                    

III. Contact time enzyme (max): 120 seconds.

Good quality of apples, chopper: small paticles.

Enzyme 600 g/ton apples.

Temperature 60° C. at the place of addition.

    ______________________________________                                                  Average Free run                                                              consistancy                                                                           juice       Mouthfeel                                       ______________________________________                                        No enzyme   6.26      ++          good                                        (before test)                                                                 With enzyme 5.75      -           very good                                   No enzyme   6.32      ++          good                                        (end of trial)                                                                ______________________________________                                    

It can be seen that through the addition of pectinesterase, without anyalterations to the apple sauce production process, the taste of theapple sauce can be improved.

The criterium of consistancy is the most important for grading differentapple sauce preparations, it is related directly to the level andquality of pectine in the apple. The industrial trials show animprovement of the consistancy of the apple sauce after the use ofpectinesterase.

In addition to the increase in consistancy an improvement of mouthfeelwas observed. Furthermore, the absence of free run juice is another signof increased quality of the apple sauce upon usage of pectinesterase.

The difference between the starting values is due to the fact that themeasurements have been performed at three different productionfacilities, the apples were not the same brand and possibly from adifferent season.

EXAMPLE 4

Effect of pectinesterase on consistancy at different dosage

One gallon can of apple sauce was recovered from the canning line(Example 3, second trial) before cooling and at a temperature of 65°-70°C.

Four trials have been performed on 500 gram samples of apple sauce. Thetrials consisted in the addition of different amounts of pectinesterase.The mixtures were kept at 60° C. for 10 minutes, subsequently thetemperature was raised to 92° C. in a microwave oven. The consistancyand the amount of free run juice were measured as described in Example3.

    ______________________________________                                        Trial    dosage     consistancy                                                                             free run juice                                  ______________________________________                                        1        control    5.70      +                                               2        200 g/ton  5.0       -                                               3        400 g/ton  4.85      -                                               4        600 g/ton  4.50      -                                               ______________________________________                                    

The results indicate that the quality of the apple sauce is furtherimproved, as evidenced by the consistancy and the amount cf free runjuice, by increasing the reaction time and concentration of thepectinesterase.

Values below 5.5 can easily be reached and this value is considered tobe of importance in pricing of the product.

EXAMPLE 5

Effect of oectinesterase on consistancy at different temperatures

The apple sauce was recovered from the canning line as described in theprevious example. The apple sauce (500 gram samples) was heated to theindicated temperatures and pectinesterase was added in an amount of 400g/ton. The samples were left to cool. Consistancy, free run juice andmouthfeel were determined as described in Example 3.

    ______________________________________                                        Trial                                                                              temperature consistancy                                                                             free run juice                                                                          mouthfeel                                ______________________________________                                        1    control     5.70      +         good                                     2    82° C.                                                                             5.45      -         good                                     3    75° C.                                                                             5.30      -         very good                                4    70° C.                                                                             5.0       -         very good                                5    65° C.                                                                             gel       -         --                                       6    60° C.                                                                             gel       -         --                                       ______________________________________                                    

The results indicate that the consistancy, free run juice and mouthfeelimprove upon using pectinesterase. This effect is temperature dependentas can be expected for enzyme activities.

We claim:
 1. A method to prepare a food containing a gel oflow-methoxylated pectin of at least one fruit or vegetable which methodcomprises:adding pectin esterase to the fruit or vegetable or to thepulp thereof in an amount effective to demethoxylate pectin; maintainingsaid fruit or vegetable or pulp under conditions such that said pectinesterase converts high-methoxylated pectin of said fruit or vegetable orpulp to low-methoxylated pectin and said low-methoxylated pectin forms agel; and formulating the fruit or vegetable or pulp to obtain thedesired food comprising said gel.
 2. The method of claim 1 wherein saidfruit or vegetable contains high-methoxylated pectin.
 3. The method ofclaim 1 wherein the fruit is apple, strawberry, orange, peach, pear,apricots, raspberry or blackcurrant.
 4. The method of claim 1 which isconducted in the absence of additional gelling or thickening agents. 5.The method of claim 1 wherein the pectin esterase is of fungal origin.6. The method of claim 5 wherein the fungus is Aspergillus.
 7. Themethod of claim 1 wherein the pectin esterase is added in purified form.8. The method of claim 1 further comprising the step of adding calciumchloride prior to allowing said low methoxylated pectin to form a gel.9. The method of claim 1 wherein said food is selected from the groupconsisting of jams, jellies, compotes, sauces and soups.
 10. A processfor converting a fruit or vegetable or pulp thereof containinghigh-methoxylated pectin into a food product having increased viscositywhich process comprises:adding pectin esterase to a liquid-containingcomposition comprising the fruit or vegetable or pulp thereof in anamount effective to demethoxylate high-methoxylated pectin; maintainingsaid liquid-containing composition under conditions such that saidpectin esterase converts at least some of said high-methoxylated pectinto pectin with a lower degree of methoxylation and said pectin with alower degree of methoxylation increases the viscosity of saidliquid-containing composition; and formulating said liquid-containingcomposition to obtain the desired food product having increasedviscosity, which food product comprises said fruit or vegetable or pulpthereof and said pectin with a lower degree of methoxylation.
 11. Aprocess according to claim 10 wherein the fruit is apple, strawberry,blackcurrent, orange, peach, pear, apricots or raspberry.
 12. A processaccording to claim 10 wherein said pectin esterase is added in an amountof between 50 and 500 PE units per kilogram of fruit or vegetable orpulp.
 13. A process according to claim 10 wherein said food product isselected from the group consisting of jams, jellies, compotes, saucesand soups.
 14. A process according to claim 10 wherein said food productis a filling for a chocolate, cake or sweet.
 15. A process according toclaim 10 wherein after adding said pectin esterase saidliquid-containing composition is maintained under conditions such thatsaid pectin esterase converts high methoxylated pectin to pectin with alower degree of methoxylation for not more than about ten minutes. 16.The process according to claim 10 wherein said pectin esterase isobtainable from a fungus which is a species of Aspergillus.
 17. Aprocess according to claim 10 for converting apples to applesauce havingincreased viscosity, which process comprises(a) adding to aliquid-containing composition consisting essentially of prepared applesan amount of pectin esterase effective to lower the degree ofmethoxylation of pectin contained in said apples wherein the apples havebeen prepared by peeling and removal of the core, removing bad apples,and crushing, chopping or slicing the remaining apples; (b) maintainingsaid composition under conditions sufficient for the demethoxylationactivity of said pectin esterase to produce an increase in the viscosityof said composition; and (c) steam cooking the apples treated as setforth in (a) and finishing in a process which comprises removingundesired particles, adding sugar and canning.
 18. The method of claim17 comprising the additional step of placing the treated apples of step(a) in a holding tank prior to the steam cooking step of step (c).